Driving rotation of rotary index tables has previously been accomplished by the use of worm gear sets. For example, U.S. Pat. No. 3,941,014 Benjamin et al and U.S. Pat. No. 4,159,658 Parkinson disclose straight worm gear sets that rotatively drive associated rotary tables during index in association with crown gears that provide positioning after the rotation. Furthermore, machine table movement has previously been provided by double enveloping worm gear sets such as disclosed by U.S. Pat. No. 3,824,892 Bondie et al and, as disclosed by U.S. Pat. No. 4,653,739, has been utilized to provide rotary positioning of a workpiece table. Such double enveloping worm gear sets have surface-to-surface contact as opposed to line contact provided by straight worm gear sets and thus have greater capacity to provide rotational driving of greater loads for the same size unit. Rotational positioning for indexing has also been previously provided by polygonal type drive couplings such as disclosed by U.S. Pat. No. 3,507,169 Signer 10 wherein a rotary drive member having polygon surfaces distributes the driving force.
The Myles, U.S. Pat. No. 4,807,338, discloses a computer controlled hydraulic drive for an index table. The computer includes a motion controller for feeding control signals to an electrohydraulic proportional valve in accordance with a pre-selected program.
The Oketani et al., U.S. Pat. No. 5,064,044, discloses an indexing apparatus for a rotary table including a rack-pinion mechanism, an electric motor for driving a feed screw shaft and a feed nut engaging the feed screw shaft.